The subject matter disclosed herein generally relates to phase identification and in particular to characterization of a power distribution network via phase identification.
Typically, power distribution networks carry voltages in three phases that consist of 50 Hz or 60 Hz sine waves that are each out of phase by approximately 120°. The three-phase power is generated in a power plant or other power source and distributed across a wide area to provide power to multiple loads such as residences and businesses. A three-phase power transmission line generally has three transmission conductors, one for each phase, and sometimes a neutral conductor as a fourth conductor.
Utility companies experience difficulties in identifying the phase of a transmission line in the distribution network. The inability to identify the phase information of a given conductor causes operational problems such as difficulty in shifting the customer loads from one phase to another under emergency conditions, or when planning future load expansion. Further, load balancing among the three phases along the distribution network uses phase identification to operate the network effectively. Reliable phase identification would allow increased effectiveness of distribution network management and reliability.
Typically, identifying an unknown phase includes comparing data from a circuit having an unknown phase to data from a circuit having a known phase. Voltage signals from the circuits are digitized and transmitted over a phone system. A series of data conversions and transmissions required in such embodiments causes inductive and/or capacitive delays, often resulting in significant phase differences.
One method to reduce phase delays includes performing a calibration at each location to compensate for the phase lags introduced at various remote locations. However, this approach relies heavily on telephone companies that operate by route switching and signals on telephone lines that are sometimes rerouted over circuits, which may vary by hundreds of miles. The additional phase shift introduced by the time delay associated with such rerouting may affect the calibration.
Accordingly, there is a need to provide an improved method and apparatus for the identification of line phase of a power line in a three-phase power distribution network.